Edge Sharpness Vs. Application

This Forum is a place for students of swordsmanship to ask advice from moderators Paul Champagne & Scott M. Rodell on how to practice test cutting in a manner consistent with how swords were historically used in combat. Readers use this Forum at their own risk.

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Re: Edge Sharpness Vs. Application

Post by Nik » Sat Jun 19, 2010 5:02 pm

As far as I was told by metallurgy experts from the german knife making forum, the type of crystallization leading to different carbide sizes also play a role in "how" an edge cuts, and how it holds up.

BTW, also a tool edge (like axes) was never polished in exact V-shape in Germany, it was always what Scott calls a ballistic edge. A bigger axe making company even has a sticker on their axes showing the V-shape with a red cross over it, and the ballistic shape with an exclamation mark (at least that was what my polisher told me).

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Re: Historically Accurate Edge Sharpness

Post by KyleyHarris » Sat Jun 19, 2010 8:58 pm

Scott M. Rodell wrote:
So Kyle, would you define edge sharpness as having 2 components, the angle of the blade surfaces & the smoothness of the metal (i.e. the grind finish)?

BTW, thanks for your straight forward critique of my Hanwei Cutting Jian...
Well. In simplest form yes. the polishing process (what many call sharpening, as I do myself) is what forms the edge and surface protection of the metal. The shape of the bevels then creates the strength and support structure for the tool.

I'm going to link to a couple of images from a video done by a friend of mine who owns many of my knives among others

This first image shows an edge that is quite jagged, and has a lot of striations. I think its a benchmade knife sharpened with a ceramic stone of some kind. now to the human eye this may well look sharp, and feel sharp to the finger, and even cutting. The problem with an edge which has this level of coarse finish is that the little teeth and jagged pieces left exposed are easy to chip out, bend, role, and pretty much destroy. After repeated cuts and blows you result in an edge which is rolled over and quite inneffective at sinking into targets.
Image

this second image shows an edge with a better level of refinement. the line where the 2 bevels meet is cleaner, and has less exposed particles of metal. under sustained use this is harder to chip, roll or fold out. This was sharpened by me using 1000grit paper and stropping
Image


The video made by a friend of mine in Japan is quite good for showing the difference between some edges under a microscope.
http://www.youtube.com/watch?v=IH4IL1RUAYk and it shows clearly the difference between basic edge grinding and a polished convex edge. the 3rd knife is made by me with a convex edge.

Now the important thing about the apex of the bevels is that the more polished and more refined it is, then the stronger and more durable it will be against failure in the field. Its important to note that all steel suffers from rust, corrosion and micro oxidation. The finer the polish the longer the edge can stay sharp without constant honing and polishing on a strop or fine stone.

A lot of people these days tend to think that a mirror polish is for aesthetic and beauty reasons only, and that its just a costly vanity to make a blade shine like a mirror. For many wallhangers this is true. But more importantly is that the surface of the steel is no different than the apex of the edges. When a finish is left very rough, such as the Hanwei Jian, then it is more suseptible to corrosion. All those jagged grind striations increase the surface area exposed to oxygen. Worse.. it creates millions of micro cavities. When the blade gets wet and you dry it off, you are still leaving many pockets of moisture trapped in all the little cavities of the steel. So, just like the edge itself, the finer the finish the bevels and blade have then the better the steels protection against the elements. with each finer level of polish that we do to the steel, we are sealing up all the pores in the steel and making it smoother and stronger. There is less ability for the elements to wear away at the blade.

The next great value of a mirror polish, or even just a good 400grit satin finish is that it is smoother. The smoother the bevels are, and the less friction created by the bevels then the easier it is for the blade to slide through the target being cut. The best example I can give of this is a drum brake on a car. The idea is that we have a fast moving wheel. To slow it down we use a relatively coarse ceramic disc and touch surfaces. the friction created slows down the wheel. Now.. if we were to polish the drum, and the ceramic to a fine finish and apply some lubricant then it probably wouldn't work very well as a brake. a sword going through a target (whatever the target) is the same. the higher the polish on all points of contact, then the less friction created. This means that it is not slowed down. The point here is that a blade with a rough finish is kind of like a nailfile.. its scraping through and catching on things which means its effectiveness at cutting is drastically reduced. In real terms, as the Japanese are well aware, is that all other factors of a blade being equal, the higher the grind and edge polish the less energy is required to perform the same cut. in battle this means you last longer.

This following image shows roughly 2 kinds of profiles. Blue is a flat diamond style profile. Red is a bullet nose Convex Style. The black represents the target. With the Blue flat profile as its cutting it has a high surface area contact. Its essential for modern blades of this style to have a high finish otherwise when cutting targets that start hitting 3" - 6" then friction will play a big role in performance. if you also have a dull edge apex it will perform terribly.. its working through sheer thinness of profile and force.

The Red Convex pushes the target away from the bevel because its a continuously changing surface angle. The only point of contact is the portions of bevel perpendicular to the target.
Image
The other important factor is the actual shape of the convex. the more bullet nose the convex then the more protected the edge is. With a heavy bullet shape convex what actually happens is a splitting action. The Edge Bites into the material and sinks in, but then the angle of the convex bevels forces the cut material out of the way of the edge with the polish of the bevel sustaining the momentum. The convex edge is using a mixture of forcing the material apart and tension cutting. Most should be aware that if you want to cut through a limb on a tree then if you bend the limb away from the edge creating tension then as you cut it will split more readily. this is the same on skin. if you stretch skin tight before applying a scalpel it will pare away more easily because its already trying to seperate. the convex edge bevels are doing this. the bevels apply a tension to the target and then the edge pares it open.. almost like hundreds of little cuts. with a full flat profile the edge is in constant contact and high friction.

This following image highlights the importance of the Convex Profile for cutting assuming we are looking at the top bevel of a single side of a Jian.
The red is a full flat diamond profile. This will perform well with a high polish on soft targets. constant use will ruin the edge.
the Green is a mild convex. with a high polish this is going to be stronger and perform better than the flat. It should also actually cut targets better because of less friction and very little deviation from the flat. The cutting edge itself at the apex can have 2-3 times more steel bolstering the cutting edge.
The Black area is a very heavy convex. This is going to be a bit harder to cut into targets, but far more durable.
the Blue Line represents a heavy Edge spine (meaning a lot more steel behind the edge) this is still razor shaving sharp, but will act more like a splitting maul and be more capable against armour and targets. This grind style quickly forces the Cut material out of contact with the edge, and a polished bevel is extremely important. because the bevels are forcing the edge out of contact with the edge it means the edges primary purpose is to make the split and after that moment the blade is ripping the target open through speed and momentum and on soft targets you get dramatic tension cutting. This is the best style of edge for a sword that will be in constant battle and hitting armoured targets. It will still cut to the bone, but it wont roll, chip, or get stuck in armour because it wont bite so deep.
Image


with a profile such as the Jian, the most important areas for a mirror polish are the Spine, and the edge. these 2 points are where the most friction will be. the rest of the bevel will benefit from smoothness for corrosion protection more than anything.


Sorry this is long winded and a little rambling. its not the simplest thing to explain without video and diagrams.

EDIT:
I feel it important to add that historically speaking.. I imagine the world was little different from today and finance played a big factor. A general, or rich person probably had something equivalent to a $2000+ Sword with all the best features, where-as the common soldier was probably fitted with something of the quality of a Hanwei Jian. How many Battles was a soldier going to encounter and actually fight in? 10? 20? for a royal treasury replacing a Hanwei quality blade every 2 or 3 battles probably made it worth it to make lower grade weapons. A High finish or low finish still cuts an arm off. A little rust on the blade, or a lot of rust would still last out the fight or even a few years of fighting. whereas a gentleman or scholar who may only take out his weapon a few times in his life for actual battle would spend more money on the highest of quality, and the best polish. They would also get a blade with a leaner convex for cutting flesh because its likely that they wouldn't need to have a sustained battle against armoured people. They would get a blade to pass down to family as an honorable item. As has been pointed out repeatedly, a lump of sharpened soft iron will work just fine in war.. These days we see soldiers fitted with Cheap as dirt Ontario Ka-Bars for a backup, not hand-made laminated quality blades of 10 times the value.. I imagine it was the same back then.. Each smith and each Martial artist probably selected edge geometries to suit their needs and styles and budget.
Last edited by KyleyHarris on Sat Jun 19, 2010 9:25 pm, edited 1 time in total.

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Re: Edge Sharpness Vs. Application

Post by KyleyHarris » Sat Jun 19, 2010 9:16 pm

Nik wrote:As far as I was told by metallurgy experts from the german knife making forum, the type of crystallization leading to different carbide sizes also play a role in "how" an edge cuts, and how it holds up.

BTW, also a tool edge (like axes) was never polished in exact V-shape in Germany, it was always what Scott calls a ballistic edge. A bigger axe making company even has a sticker on their axes showing the V-shape with a red cross over it, and the ballistic shape with an exclamation mark (at least that was what my polisher told me).
Yes. The size of the carbides in the matrix plays a big role in how it holds up. This is why modern powder steels such as CPM 3V are so good. They get the mix very very small and consistent which makes the steel tougher, and harder wearing and less prone to bigger carbides chipping out of the edge. With steels that have bigger carbides as part of their make up a toothy edge makes it much easier to knock the edge off. Its like Stone walls built using large mixtures of different sized stones and held together with mortar. if the top of the wall was not finished and smoothed nicely with mortar than attacking objects hitting the wall easily chip and flake and tear chunnks out of the wall exposing the pieces underneath.. The smooth surface makes it all tougher.

I've never heard of an Axe the does not have a convex edge, unless its a cheap mass produced one. Until the modern age of manufacturing where we can easily create flat grinds and flat edges with machines to make dirt cheap knives the flat edge was almost unheard off. The convex edge has been pretty much the standard for millenia since the days of flint napping. Production companies dont use convex for a singular reason.. they cannot automate the process.. they cannot mass produce cheap items.

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Re: Edge Sharpness Vs. Application

Post by KyleyHarris » Sat Jun 19, 2010 9:46 pm

These videos are not directly related to Chinese Swords, but they are related to the convex edge and Application.

This was a rough and hard demonstration of edge durability of a blade. As Requested by the customer.. Yes, I actually hard test knives before I ship them to make sure they do the job. This is a 13.5" bushcrafting shortsword with a 4mm spine and a heavy convex edge.
On this particular blade I impacted aluminum poles over 30 times, and did hard hitting on dry hard wood for an hour performing hundreds of hits, as well as the bamboo etc.. The thick convex edge prooves how durable a convex can be, and also stay sharp.

Test 1 involved Beating and hard impacts against aluminum poles and testing the edge for damage and retention.
http://www.youtube.com/watch?v=_HXsjlWXTkA

Same blade with the same thick edge cutting some bamboo.. nothing huge or spectacular, its a small blade. there is also a 17" short sword of mine used which is mirror polished convex.
http://www.youtube.com/watch?v=fcQYRqKxnKo

Same blade doing some idiotic testing of edge durability.
http://www.youtube.com/watch?v=9zWIC7OBFps

Now, while these tests may seem ludicrous they are are.. but they are specifically to test the edge and steel, not a skill in cutting. I will often employ bad technique on hard hits with deflection etc.. to test the edge and blade against bad hits.

This blade is a heavier edge than the Jian, and is ridiculously sharp before and after all these tests. the steel is O1 at 57RC.

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Re: Edge Sharpness Vs. Application

Post by Scott M. Rodell » Wed May 09, 2012 3:04 pm

I was practicing in my garden this morning with my Cutting Jian. As I turned to deliver a pi cut, I spontaneously decided to cut an oak leaf on at the end of a nearby branch. My blade sliced cleanly thru it, leaving the leaf on the branch. That action brought to mind those words above, written so long ago by Paul. My Cutting Jian was polished beyond the standard factory polish by Philip Tom. But it is not what Paul called "eye popping" sharp. I believe Phil took it to 600 grit, what we would call a working polish. Yet it sliced clean thru the loosely hanging leaf. Once again I thought, today in the martial arts world, we tend to think swords need to be sharper than they really need to be, to cut.

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Re: Edge Sharpness Vs. Application

Post by taiwandeutscher » Wed May 09, 2012 10:52 pm

Agreed! When the technique is right, the cutting can be soothly done with a not so super sharp blade.

What I alsways wonder:
Why did the Japanese Katanas show such a sharpness? Or maybe that's a mis-information? Cutting the flowting leaf in the water, just by getting onto the still held blade?
hongdaozi

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Re: Edge Sharpness Vs. Application

Post by Scott M. Rodell » Tue Dec 04, 2012 7:58 am

taiwandeutscher wrote: ... I always wonder:
Why ... the Japanese Katanas ... sharpness?...
I believe the function of very sharp blades was to be able to cut fabric in self-defence situations, i.e. one on one or one vs. multiple opponents, off the battlefield. In such situations, one's attackers are unlikely to be wearing any sort of hard armor that could distort or damage the swords edge, so a sharp edge can be used. And that sharp edge will help cut thru everyday clothing, keeping in mind that cloth has a strong braking action to any cut. Just consider how difficult it is to draw cut thru a t-shirt loosely laid over a cutting board.

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